Former Republican presidential nominee Mitt Romney has emerged as a star on the GOP fundraising circuit. (Jacquelyn Martin/AP)

One rainy morning this month, the man who thought he would be president boarded a train near his beach house in San Diego. He stepped off in Burbank, Calif., and caught a ride to a sound stage, where his on-again, off-again political consigliere, Mike Murphy, was waiting to shoot a commercial on a set that bore more than a passing resemblance to the Oval Office.

Looking and sounding like a president out of central casting, he nailed his lines. The crew called him “one-take Romney,” and before he departed, they swarmed, extending arms around his shoulders and angling their iPhones for pictures.

With that, Mitt Romney’s long winter was over.

After retreating from public view following his crushing loss to President Obama in the 2012 election, Romney has returned to the political stage, emerging as one of the Republican Party’s most coveted stars, especially on the fundraising circuit, in the run-up to November’s midterm elections.

He may not direct a high-powered political action committee or hold a formal position, but with the two living former Republican presidents — George H.W. Bush and George W. Bush — shying away from campaign politics, Romney, 67, has begun to embrace the role of party elder, believing he can shape the national debate and help guide his fractured party to a governing majority.

Insisting he won’t seek the presidency again, Romney has endorsed at least 16 candidates this cycle, many of them establishment favorites who backed his campaigns. One friend said he wants to be the “anti-Jim DeMint,” a reference to the former South Carolina senator and current ­Heritage Foundation chairman who has been a conservative kingmaker in Republican primaries. Romney’s approach is to reward allies, boost rising stars and avoid intraparty conflict.

Romney has signed his name to sharply partisan e-mail appeals and headlined recent fundraisers from Las Vegas to Miami to Boston. This week, he appeared in his first television ad: a U.S. Chamber of Commerce spot supporting Rep. Mike Simpson (R-Idaho), who faces a tea party challenger in a state where Romney remains widely popular. And Romney’s confidants said he will appear in more ads, record robo-calls and stump at rallies later this year.

“He believes in the cause, he wants us to win the House and Senate, and he wants to be useful,” said Murphy, who oversaw production of the Simpson ad on April 2.

Tom Rath, a New Hampshire-based former Romney adviser, added: “He never said he would take a vow of political abstinence. . . . He is a man at peace, but I don’t think that he has politics totally out of his blood.”

Although Romney tries to silence such speculation, his resurfacing has spurred chatter among elite financiers and operatives that he is eyeing a comeback in 2016. On March 25, Romney visited New York to raise money for Ed Gillespie, a former adviser who is running for the U.S. Senate in Virginia. Sitting around the dining table in the Park Avenue home of private equity titan Stephen A. Schwarzman, Romney poked fun at some of his campaign trail missteps and, according to attendees, assured the two dozen donors that he would not run again.

Romney is heartened, his intimates said, that the GOP has not cast him aside as a loser. Spencer Zwick, the 2012 campaign’s national finance chairman, who is so close to the family that Romney calls him his “sixth son,” said he believes Romney has become more popular over the past six months than he was during the election.

“The level of interest in him has skyrocketed,” Zwick said. “I think there is an enormous sense of buyer’s remorse, that he was right on Russia and a whole range of issues. I believe if the election were held today, he would win.”

In the first weekly edition of Costa Reports, Robert Costa explores why this may be Paul Ryan's moment and the internal conflict he's facing about his political future. (Jeff Simon/The Washington Post)

Former Minnesota governor Tim Pawlenty, who became a Romney surrogate in 2012 after clashing with him in the early GOP primaries, said that Romney is poised to “remain a leading voice in the party for a long time to come” and that he is “way too young, smart and service-oriented to just fade away.”

But some conservative activists would rather see Romney disappear. Asked about Romney’s moves, organizer Richard Viguerie quipped, “It seems like ‘Groundhog Day.’ ”

L. Brent Bozell III, chairman of ForAmerica, a conservative advocacy group, said: “His career is finished. He ran an astonishingly inept campaign, and it is fine if he wants to be a senior statesman for the party. But I hope he’s not trying to advance himself or his moderate philosophy. That would be destructive.”

Romney has downsized his once vast political operation to a single aide, Kelli Harrison, and his inbox and cellphone. He keeps up on political developments with a small cadre of loyal former advisers and regularly consults Sen. Rob Portman (R-Ohio), who stood in for Obama in his debate preparations, and Rep. Paul Ryan (R-Wis.), his 2012 running mate. Ronna Romney McDaniel, his niece and one of Michigan’s members of the Republican National Committee, keeps him updated on party affairs.

Romney also exchanges e-mails with New Jersey Gov. Chris Christie (R). In late February, when the two appeared at a Republican Governors Association fundraiser at the Lenox Hotel in Boston, Romney pulled Christie aside to remind him to attend his June summit in Utah. The conclave in Park City, where Romney purchased a sprawling ski chalet last year, will be a reunion for Romney’s major donors and top aides, as well as a sales session for Solamere Capital, the private equity firm run by Zwick and Romney’s eldest son, Tagg.

Romney has invited most prospective 2016 Republican presidential candidates to attend. Instead of hosting another cattle call showcasing well-rehearsed ­pitches, Romney is giving this year’s retreat a theme: the future of American leadership, at home and abroad. He has asked the featured guests to tailor their remarks around it.

Sen. Rand Paul (Ky.), former Arkansas governor Mike Huckabee and Ryan will make the trek to Utah, as will Portman. Former Florida governor Jeb Bush declined because of a scheduling conflict.

Eric Fehrnstrom, a longtime aide who still counsels Romney, said the event is “an important touchstone” for the Romney network.

“Mitt Romney was the first Republican candidate to raise $1 billion for a campaign,” Fehrnstrom said. “That is the new bar. And I think Mitt’s personal help and the support of his network is going to be crucial in helping the next Republican candidate for president achieve that $1 billion mark and hopefully surpass it.”

Scores of candidates in the midterm elections have sought Romney’s endorsement, including Mark Hutchison, a Nevada state senator and fellow Mormon who is running in a June primary for lieutenant governor against former state party chairwoman Sue Lowden.

On March 20, Romney visited Las Vegas to raise money for Rep. Joseph J. Heck (R-Nev.), a Romney supporter in 2012, at the home of businessman Travis Brady. There, Hutchison approached Romney and asked for assistance.

“We went over what I have been doing as an attorney to fight Obamacare in the courts, and after we finished our brief conversation, he said he’d be in touch,” Hutchison said.

As with other such requests, Romney consulted his informal circle of advisers. These conference calls often include his former business partner, Bob White, and former aides Fehrnstrom, Stuart Stevens, Russ Schriefer, Matt Rhoades, Beth Myers, Peter Flaherty, Ron Kaufman and Lanhee Chen.

On Monday, Romney wrote a letter endorsing Hutchison, calling him a “champion for Nevadans’ constitutional rights.”

Romney doesn’t say yes to every entreaty. In Illinois, state Treasurer Dan Rutherford and businessman Bruce Rauner each pressured Romney to endorse his gubernatorial primary. For weeks, Romney mulled weighing in, but he decided to sit out the primary — even though in 2012, Rutherford was Romney’s state chairman and helped him beat former senator Rick Santorum in the Illinois primary.

A map of Romney’s other stops and endorsements is a reflection of his relationships and his tendency toward even-tempered fiscal hawks. “He’s looking for pragmatic conservatives,” said former Minnesota senator Norm Coleman, a Republican. “It’s not so much about scoring political points with every segment of the party but about finding people who, like him, understand the need for governing.”

In the first quarter of this year, according to his federal filing, Romney donated to Elise Stefanik, a former Ryan aide who is running for a House seat in New York; to Steve Daines, a Montana Senate candidate who has been encouraged by Portman; and to state Sen. Tony Strickland, a former Romney state chairman who is seeking an open House seat in southern California. In Iowa, after his former state adviser David Kochel reached out to him, Romney endorsed state Sen. Joni Ernst, a GOP Senate candidate and the only elected official in a crowded primary.

In Virginia, Del. Barbara J. Comstock (R-Fairfax), who is running for the seat of outgoing U.S. Rep. Frank R. Wolf (R), worked on Romney’s 2008 campaign and was a key surrogate in 2012. She received a supportive Twitter message from Romney in January and $2,000 from him in March.

Romney is also backing Scott Brown, the former U.S. senator from Massachusetts who is running this year in New Hampshire. Romney and Brown share several advisers, including Ryan Williams, who said he hopes the two march together on July 4 in a parade in Wolfeboro, where the Romney family vacations on Lake Winnipesaukee.

On June 9, Romney is scheduled to attend a reception at the Metropolitan Club in New York hosted by the National Republican Senatorial Committee to help raise money for Brown and other GOP Senate contenders.

Romney’s appeal has limits, though, especially in states with a more conservative tilt. In South Carolina, Sen. Lindsey O. Graham has not sought his support in his competitive primary, nor has Romney helped Gov. Nikki Haley, a Romney endorser in 2008 and 2012.

Romney advisers said he is willing to help Sen. Thad Cochran fend off a tea party challenger in Mississippi, but Cochran has not asked. “It’s not in the playbook right now,” a Cochran adviser said.

Robert Shrum, who advised unsuccessful Democratic presidential nominees Al Gore and John F. Kerry, said that Romney wants “significance” but that “he can be more helpful at this point with money than electorally. The clearest instance to me of the situation is the decision of [Ohio Gov.] John Kasich to airbrush him out of his ad.”

As the Columbus Dispatch reported last week, Kasich’s gubernatorial campaign scrubbed a Romney placard from Kasich’s campaign Web site. Romney lost Ohio to Obama.

Romney is more welcome in Idaho. Strategist Scott Reed said that when the Chamber of Commerce surveyed voters recently, it found that Romney’s approval rating among Republicans in Simpson’s district was a whopping 86 percent. So Reed asked Kaufman if Romney would cut an ad for Simpson, and Romney agreed.

“He was a champ,” Reed said. “It’s going to help us win this race.”

When Romney visited Boise and Idaho Falls in March for events helping Gov. C.L. “Butch” Otter, Sen. James E. Risch and Simpson — all former Romney backers — he felt at home. Gone were his campaign entourage and Secret Service agents.

“He decided to go jogging by himself, out on the greenbelt trail along the Snake River,” Otter said. “When he got back, he told me he just loved sucking up all that good, clean oxygen. He may have been here for politics, but that run can be a tonic, and he liked that tonic.”